The present specification relates to a semiconductor device and a method of making a semiconductor device.
In recent years, GaN/AlGaN High Electron Mobility Transistors (HEMTs) have drawn a lot of attention regarding their potential to replace Si or SiC for use as high voltage (HV) devices. A GaN/AlGaN HEMT typically includes a substrate having an AlGaN layer located on a number of GaN layers. A gate, source and drain are located above the AlGaN layer. During operation, current flows between drain and source via a two-dimensional electron gas (2DEG) that is formed at the interface between the AlGaN layer and an upper GaN layer. Switch-off is achieved by applying a suitable voltage to the gate, such that the 2DEG at the interface between the AlGaN layer and the uppermost GaN layer disappears.
In some applications, these devices are switched between an off state, where they block a high drain-to-source voltage while having a low leakage current, and an on-state, where they carry a high current at a low voltage. The design of these devices is such that an optimum trade-off may be found between the power losses in the on-state, off-state and during switching.
Two different gates are typically used in HEMTs. Firstly, the gate may be a Schottky gate, comprising a Schottky contact located on the AlGaN layer. An alternative type of gate is an insulated gate, in which the gate contact is separated from the surface of the AlGaN layer by an insulting layer. Devices including this second type of gate are referred to as Metal Insulator Semiconductor High Electron Mobility Transistors (MISHEMTs). A potential advantage of the MISHEMT is a lower leakage current in the off-state.